The invention relates to improvements in power trains for use in motor vehicles. More particularly, the invention relates to improvements in power trains which, in addition to transmitting torque to the wheels of a motor vehicle by way of a suitable transmission assembly, are called upon to transmit torque or power or motion to one or more auxiliary aggregates, e.g., to the pump of a power steering system, to a light generator, to a component part (e.g., a compressor) of an air conditioning system, and/or others.
It is already known to construct the power train in a motor vehicle in such a way that a prime mover (such as an internal combustion engine) transmits torque to an energy storing torque transmitting device (e.g., a flywheel) in response to engagement of a first clutch, and the torque transmitting device can drive the rotary input member of a transmission assembly in response to engagement of a second clutch. Furthermore, the power train is designed to drive at least one first and at least one second auxiliary aggregate. Reference may be had, for example, to published German patent application No. 44 44 545 which discloses a power train for a motor vehicle wherein, as a rule, the auxiliary aggregates are driven directly by the prime mover. In other words, if the prime mover is off (e.g., while a motor vehicle is coasting), the auxiliary aggregate or aggregates is or are invariably idle.
A drawback of such prior proposals is that the operation of an auxiliary aggregate which is not driven at all times while the motor vehicle is in use (or which is idle for extended periods of time or which is idle at inopportune times) is likely to be adversely affected and is likely to operate unsatisfactorily, or to become inoperative, with attendant danger of inconvenience to the occupant or occupants of the motor vehicle. For example, a defective braking force amplifier is likely to endanger the occupant or occupants of a motor vehicle by failing to operate in a desired manner while the combustion engine is turned off or as a result of repeated starting and stoppage.
On the other band, certain auxiliary aggregates are not affected, or not unduly affected, by repeated stoppages and/or by prolonged idleness; in fact, it might even be advisable or useful to maintain such auxiliary aggregates at a standstill for extended intervals of time while the motor vehicle is in use.